<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .www{
            width: 50px;
            height: 30px;
            background-color: lime;
            display: none;
        }
        li:hover .www{
            display: block;
        }

    </style>
</head>
<body>
    <ul>
        <li>ddddddd
            <ul class="www">
                lllll
            </ul>
        </li>
    </ul>
</body>
</html>